Method for the post-injection of hydrocarbon-, alcohol- and/or reducing-agent-type regeneration solution (e.g. diesel fuel and/or urea and/or ammoniacal solution) for the regeneration of diesel engine exhaust gas filtration systems

ABSTRACT

A post-injection method for the regeneration of a device used to filter diesel engine exhaust gases. The method includes injecting a fully-pulverised hydrocarbon-, alcohol- and/or reducing-agent-type regeneration solution upstream of the oxidation catalyst ( 14 ) to increase the exhaust gases&#39; temperature upon detection of clogging of the filter with particles. A computer uses temperature ( 2 ) and pressure ( 3 ) sensors disposed upstream of the filtration device to control injection of the regeneration solution from an electromagnetic injector ( 9 ). The regeneration solution is directed through a capillary ( 12 ) into the exhaust pipe ( 1 ) at a point located at a good distance from the injector, upstream of the catalyst ( 5 ), in order to be finely pulverised by the air.

The present invention relates in general to the field of particulatefilters and, more particularly, to a method for the post-injection of ahydrocarbon-, alcohol- and/or reducing-agent-type regeneration liquid(e.g. diesel fuel and/or urea and/or ammoniacal solution) upstream of adiesel engine exhaust gas filtration device to regenerate this filter.

Moreover, the present invention further relates to the management ofthis injection device, of which the purpose is to inject a homogeneousmixture of air and hydrocarbon-, alcohol- and/or reducing-agent-typeregeneration liquid (e.g. diesel fuel and/or urea and/or ammoniacalsolution) on the oxidation catalyst upstream of the filtration system toincrease the temperature of the exhaust gases, as for a combustion. Ahigh temperature level is necessary to oxidize and burn the carbonaceousparticles produced by the engine and retained on this filtration system,in order to prevent their accumulation, this final phase constitutingthe regeneration, the object of the method according to the invention.

In addition to the development of new engines with lower and lower fuelconsumption, a special effort has been made for the development of newexhaust systems, designed to reduce the emission of unburnt pollutantgases and solid particulates. Thus automobile manufacturers havedeveloped catalytic converters or catalysts, generally consisting of astainless steel housing, a thermal insulation and a honeycomb supportimpregnated with precious metals such as platinum or rhodium. Thesecatalysts make it possible to reduce, above all, the emissions ofpolycyclic hydrocarbons and CO, in a proportion of about 90%. However,they exert no action on emissions of solid particulates. Thus,particularly for diesel engines which produce numerous solidparticulates, these catalysts provide no significant improvement in airquality.

Other techniques have been developed to limit the emission of pollutantparticulates by vehicles. One such case is the particulate filter. Thisfilter serves to reduce the total mass of particulates emitted by dieselengines by more than 90%.

However, the particulate filter requires regeneration in order to burnthe particulates that have been trapped. The particulates are generallytrapped by a filter cartridge forming part of the particulate filter. Towithstand the high temperatures encountered, this cartridge may consistof a porous body of cordierite, quartz or silicon carbide, generally ina honeycomb structure to present a maximum filtration surface area.

The major difficulty of the operation of these particulate filtersresides in the control of the phase of oxidation and combustion of theparticulates retained by the filter cartridge. In fact, in urban drivingconditions, the temperature reached by the exhaust gas is insufficientto cause their combustion and to significantly limit the clogging of thefilter and hence its regeneration. Without chemical assistance, thecarbonaceous particles produced by the combustion of diesel fuel indiesel engines only begins to oxidize significantly above 500° C. Thesetemperatures are practically never reached in urban driving conditions.

It therefore appears necessary to resort to a chemical method to removethese particulates. Various techniques are used to obtain theircombustion.

A first technique consists in arranging a catalyst upstream of thefilter, to oxidize the nitric oxide (NO) present in the exhaust gases tonitrogen dioxide (NO₂), the latter having the property of catalyzing thecombustion of the carbonaceous particles from 250° C. However, thismethod requires the use of a diesel fuel in which the sulfur content islower than 50 ppm (parts per million), to preserve sufficient NO to NO₂conversion efficiency.

This technique, called “Continuous Regenerating Trap” (C.R.T.) combinesthe effects of the particulate filter and the NO oxidation catalyst. Toguarantee satisfactory operation of the filters, this system requiresregular regeneration to limit the pressure drop across the filter whileeliminating the risk of uncontrolled and exothermic regeneration.

In the opposite case, violent reactions occur, associated with theexcessive concentration of carbonaceous particles clogging the filter.These reactions consist of the excessively rapid combustion of a largemass of particles, generally causing destruction of the filter bythermal shock, because of the very high temperatures reached locally.

Other techniques make use of organometallic additives added to thediesel fuel, such as cerium, iron, strontium, calcium or others. Thesetechniques serve to obtain a similar effect to the one obtained withNO₂, by catalyzing the combustion of the carbonaceous materials attemperatures close to 370° C.

A first drawback of these techniques is the prohibitive cost of theadditives used.

Another major drawback is the necessity to provide a supplementarydevice for introduction of the additive.

A further drawback of these techniques is that they exhibit an evengreater tendency to clogging of the filter and hence the resultingreactions, if the temperatures reached in operation are not sufficientlyhigh, since the additives present in the carbonaceous materialscontribute to an even faster fouling of the filter medium.

Other techniques have consisted in experimenting with devices based onsupplementary heating means such as burners, electric resistors andothers. These supplementary heating means are only used if the cartridgeexhibits incipient clogging, reflected by an increase in the pressuredrop. Such a regeneration device is put into practice with the enginerunning, that is, in the presence of a high exhaust gas flow. Such adevice hence requires considerable heating power to simultaneously raisethe exhaust gases and the mass of the filter cartridge to the righttemperature.

On recent so-called common rail diesel engines, a diesel fuelpost-injection technique has been used to increase the temperature ofthe exhaust gases and thereby significantly oxidize and burn thecarbonaceous particles retained on the filter. This direct injectiontechnique, which makes use of electromagnetic injectors, effectivelyserves to proceed with a new diesel injection into the combustionchamber at the time when the exhaust valve opens and thereby to obtain ahomogeneous mixture with the exhaust gases and complete oxidation ofthis diesel fuel on the oxidation catalyst positioned between the engineoutlet and the particulate filter.

Also known are methods for the post-injection of regeneration liquid ofthe diesel fuel and/or alcohol type, for the regeneration of thefiltration means arranged downstream of the combustion catalysts indiesel engine exhaust systems. These methods are described in particularin the following patent applications and patents: U.S. Pat. No.5,207,990, EP-A-1 158 143, U.S. Pat. No. 6,023,930, JP-A-07 119444 andU.S. Pat. No. 5,522,218.

These known methods have the common feature, on the one hand, of notpermitting optimal, safe and economical regeneration of the filtrationmeans, and, on the other, of providing no satisfactory solution to thetechnical problem of the thermal degradation and coking of theregeneration liquid, particularly as regards diesel fuel, and especiallyat the level of the nozzles of the injectors belonging to thepost-injection means. The post-injectors are thereby rapidly damaged bythe heat of the exhaust manifold and are hence neither reliable, noreffective.

In such a technical context, it is the object of the present inventionto provide a method for the post-injection of hydrocarbon-, alcohol-and/or reducing-agent-type regeneration liquid (e.g. diesel fuel and/orurea and/or ammoniacal solution) adaptable to all diesel engines,permitting regeneration of a filtration device, which remedies thedrawbacks of the various existing techniques, consisting in treating thecarbonaceous particles and soot emitted by the diesel engines byincreasing, whenever necessary, the temperature of the exhaust gases toobtain the right oxidation temperature.

A further object of the invention is to provide a method for thepost-injection of hydrocarbon-, alcohol- and/or reducing-agent-typeregeneration liquid (e.g. diesel fuel and/or urea and/or ammoniacalsolution), thereby avoiding any risk of accumulation of particulates inthe filtration device and hence any risk of uncontrolled regeneration.

A further object of the invention is to provide a method for thepost-injection of hydrocarbon-, alcohol- and/or reducing-agent-typeregeneration liquid (e.g. diesel fuel and/or urea and/or ammoniacalsolution), which is not subject to the technical problem of thermaldegradation and coking of the regeneration liquid, particularly asregards diesel fuel, and especially at the level of the nozzles of theinjectors belonging to the post-injection means.

A further object of the invention is to provide a method for thepost-injection of hydrocarbon-, alcohol- and/or reducing-agent-typeregeneration liquid (e.g. diesel fuel and/or urea and/or ammoniacalsolution), not causing significant additional consumption of fuel and,in general, not incurring any additional financial cost to the user.

A further object of the invention is to provide a method for thepost-injection of hydrocarbon-, alcohol- and/or reducing-agent-typeregeneration liquid (e.g. diesel fuel and/or urea and/or ammoniacalsolution), that does not reduce the performance of the engine,particularly by pressure drops, because of the backpressure exerted bythe exhaust gases on the engine, due to the clogging of the filtrationdevice.

A final object of the invention is to provide a filtration devicepermitting the putting into practice of the method according to theinvention of post-injection of hydrocarbon-, alcohol- and/orreducing-agent-type regeneration liquid (e.g. diesel fuel and/or ureaand/or ammoniacal solution).

These objects, among others, are achieved by the present invention whichrelates, primarily, to a method for the post-injection of a regenerationliquid, particularly for the regeneration of a device for filteringexhaust gases produced by a diesel engine, this method being of the typewherein particulates, after being sent to an oxidation catalyst, areretained on a filtration means of said filtration device.

The method according to the invention is characterized

in that the regeneration liquid comprises at least one hydrocarbonand/or at least one reducing agent,

and in that this post-injection consists essentially in injecting,upstream of the catalyst, using post-injection means:

on the one hand, the regeneration liquid,

and on the other, at least one gaseous fluid, preferably compressed air,

this regeneration liquid and this gaseous fluid together forming anaerosol suitable for spraying the regeneration liquid into the exhaustgases and for increasing their temperature, so as to accelerate theoxidation rate of said particulates and thereby contribute to theregeneration of the filtration device.

The method according to the invention serves to obtain a good qualityaerosol, the indicator of very good regeneration of the exhaustparticulate filter.

In this diesel fuel post-injection method, use is made of a devicearranged at the outlet of the diesel engine exhaust gases and upstreamof an oxidation catalyst, downstream of which are situated the means forfiltration of the carbonaceous particles emitted by a diesel engine. Inthis method, the particulates retained on a filtration means are burnedby the action of the residual oxygen and nitrogen oxides present in theexhaust gases.

According to a preferred arrangement of the invention, thepost-injection stream of regeneration liquid and the post-injectionstream of gaseous fluid, preferably compressed air, issue fromsubstantially concentric openings.

According to an even more preferred arrangement of the invention, a partof the gaseous fluid, preferably compressed air, passes through the samenozzle as the regeneration liquid, up to the post-injection opening.

To further improve the quality of the post-injection aerosol, it isprovided according to the invention that a part of the gaseous fluid bemixed with the regeneration liquid before the post-injection.

One of the advantageous arrangements of the invention to limit the riskof clogging consists in maintaining the flow of gaseous fluid,preferably compressed air, in the post-injection nozzle, after theinterruption of the post-injection of the regeneration liquid throughthis nozzle, and during the time necessary for rinsing said nozzle.

To minimize the problem of coking and thermal degradation, arrangementsare made so that the temperature of at least a part of thepost-injection means is kept lower than or equal to 120° C., preferably100° C., while the engine is running.

For this purpose, at least a part of the post-injection means isadvantageously kept at a distance from the pipe(s) in which the exhaustgases flow.

Preferably, the regeneration liquid is selected: from the group ofhydrocarbons comprising oil refining products (preferably gasoline anddiesel), from the group of alcohols (preferably methanol), from thegroup of reducing agents (preferably urea and ammoniacal solutions), andmixtures thereof.

According to a preferred embodiment of the invention, the methodcomprises the following essential steps consisting in:

measuring a temperature θ_(m) upstream of the oxidation catalyst,

comparing θ_(m) to a temperature θ_(r) corresponding to the temperatureat which the combustion of the regeneration liquid, in the presence ofthe combustion catalyst, is complete,

if θ_(m) is equal to or greater than θ_(r), initiating a post-injectionof regeneration liquid.

According to an interesting variant of this preferred embodiment, it isprovided:

-   -   to measure a pressure P_(m) upstream of the filtration system by        a sensor 3, said pressure P_(m) reflecting the degree of        obstruction of the filtration means 5 by the particulates,    -   to compare said pressure P_(m) to a reference pressure P_(r)        corresponding to the maximum acceptable degree of obstruction,    -   if P_(m) is equal to or greater than the pressure P_(r) and if        θ_(m) is equal to or greater than θ_(r), to initiate the        post-injection of diesel.

It is particularly advantageous according to the invention to controlthe injections of regeneration liquid, using at least one computer,taking account of the temperature θ_(m) data and possibly the pressureP_(m) data, to obtain the temperature increase desired for optimalregeneration of the filtration device.

According to another of its objects, the invention further relates to adevice for in particular putting into practice the post-injection methodas defined above. This device comprises at least one exhaust pipe, atleast one catalyst, and filtration means. It is characterized in that itfurther comprises:

-   -   regeneration liquid supply means,    -   means for supplying pressurized gaseous fluid, preferably        compressed air,    -   post-injection means communicating with an exhaust gas exhaust        pipe including:        -   at least one injector preferably electromagnetic,        -   at least one injector-holder, on which said injector is            arranged,        -   at least one capillary or nozzle starting from the injector            and terminating in at least one exhaust pipe via at least            one opening,        -   upstream of the catalyst,        -   at least one line connected to the means for supplying            pressurized gaseous fluid, preferably compressed air, and            terminating in the exhaust pipe(s), via at least one            opening,    -   possibly at least one temperature sensor for measuring θ_(m),        arranged on the exhaust pipe(s), upstream of the catalyst,    -   possibly at least one pressure sensor for measuring P_(m) in the        exhaust pipe(s) and arranged on said pipe(s) upstream of the        catalyst,    -   at least one computer for controlling the post-injection,    -   to which are subjected the regeneration liquid supply means, the        means for supplying pressurized gaseous fluid,    -   preferably compressed air, the post-injection means, and the        temperature or pressure sensor(s), if any.

According to the remarkable features of the device according to theinvention:

-   -   the capillary (or nozzle) and the line are concentric and        coaxial, like their respective openings, which terminate in the        exhaust pipe(s),    -   and the capillary (or nozzle) is contained in the line.

Advantageously, at least a part of the post-injection means, preferablyat least the injector, is designed so that it is preferably arranged ata sufficient distance from the exhaust pipe(s) to avoid sufferingthermal damage, that is, to remain at a temperature lower than or equalto 120° C., preferably 100° C., while the engine is running.

The post-injection of the hydrocarbon-, alcohol- and/orreducing-agent-type regeneration liquid (e.g. diesel fuel and/or ureaand/or ammoniacal solution) is assisted by a pressurized gaseous fluid(for example, compressed air). Thanks to the structure of the capillary(or nozzle) line combination, the injector and its support are located:

-   -   geographically at a point distant (for example by 200 mm) from        the exhaust pipe, to avoid being subjected to high temperatures,    -   and upstream of the oxidation catalyst.

The exhaust gas filtration means are located downstream of the oxidation(or combustion) catalyst. The catalyst and the filtration means are, inpractice, contained in a chamber, which is located in the path of thestream of exhaust gases produced by an engine.

According to a preferred embodiment of the device according to theinvention, the means for supplying pressurized gaseous fluid, preferablycompressed air, are designed to permit the intake of gaseous fluid atthe outlet of the injector, at the head of the capillary or nozzle, sothat the pressurized gaseous fluid, preferably compressed air, can flowwith the post-injected regeneration liquid in the capillary or nozzle.

According to an advantageous variant of this preferred embodiment, themeans for supplying pressurized gaseous fluid, preferably compressedair, comprise a solenoid valve controlling the intake of pressurizedgaseous fluid, preferably compressed air, at the outlet of the injector,at the head of the capillary or nozzle, to permit said fluid to flowwith the regeneration liquid and, secondarily, to rinse the capillary ornozzle after the end of the post-injection, by maintaining, for sometime, a flow of pressurized gaseous fluid, preferably compressed air, inthe capillary or nozzle.

According to a further variant of this preferred embodiment, the meansfor supplying pressurized gaseous fluid, preferably compressed air, andthe post-injection means—preferably the injector-holder, are designed sothat at least one calibrated orifice is provided for the continuousintake of a flow of pressurized gaseous fluid, preferably compressedair, mixed with the regeneration liquid, at the inlet of the capillaryor nozzle, in order to produce an emulsion and further and preferably toperform the rinsing function, by maintaining, for some time after theclosure, a flow of said gaseous fluid in the capillary or nozzle.

Advantageously, the regeneration liquid supply means are connected tothe feed line of at least one mechanical injection pump of the engine.

The regeneration liquid is preferably selected:

-   -   from the group of hydrocarbons comprising oil refining products        (preferably gasoline and diesel),    -   from the group of alcohols (preferably methanol),    -   from the group of reducing agents (preferably urea and        ammoniacal solutions),

and mixtures thereof.

Remarkably, the device according to the invention comprises atemperature sensor and a pressure sensor. Furthermore the computer (orelectronic control box), which is connected to the temperature sensorand the pressure sensor, compares the values θ_(m) and possibly P_(m)measured respectively with the reference values θ_(r) and possiblyP_(r), and initiates the post-injection of regeneration liquid into theexhaust pipe, via the regeneration liquid supply means, the means forsupplying pressurized gaseous fluid, preferably compressed air, and thepost-injection means, when the measurements θ_(m) and possibly P_(m) areequal to or higher than the reference values θ_(r) and possibly P_(r).

Advantageously, the temperature sensor and, if any, the pressure sensor,are located substantially at the same level on the exhaust pipe.

In practice and for example, the post-injection is carried out by aconventional electromagnetic injector of the same type as the one usedon gasoline engines, this injector being arranged on an injector port ata distance from the exhaust pipe. The hydrocarbon-, alcohol- and/orreducing-agent-type regeneration liquid (e.g. diesel fuel and/or ureaand/or ammoniacal solution) issuing from this injector is conveyed via acapillary contained in a line consisting, for example, of a metal tube,to the hot exhaust pipe. This tube is supplied with compressed air so asto arrive concentrically around the capillary to flow into the exhaustpipe and cause proper spraying of the hydrocarbon-, alcohol- and/orreducing-agent-type regeneration liquid (e.g. diesel fuel and/or ethanoland/or urea and/or ammoniacal solution). The injection of regenerationliquid and the supply of compressed air are controlled by-the electroniccontrol box, which controls the opening/closure of solenoid valvespermitting the post-injection of regeneration liquid into the exhaustgas discharge pipe.

Advantageously, in the injector-holder, a calibrated orifice connectedwith the air intake and opposite the injector tip is arranged so as togenerate a regeneration air/liquid emulsion at the inlet of thecapillary and permit the injection of this regeneration liquid in fullyatomized form at the outlet, into the discharge pipe.

The present invention will be better understood from a reading of thedescription that follows, provided with reference to the drawingsappended hereto, in a non-limiting manner, of an embodiment of thepost-injection device incorporated in a filtration system according tothe invention and in which:

FIG. 1 shows a general schematic view of the system comprising thefiltration device with its oxidation catalyst and, upstream of thisassembly, the post-injection system for putting the regeneration methodinto practice.

FIG. 2 shows a detailed view of the post-injection device according to afirst embodiment.

FIG. 3 shows a detailed view of a variant of the post-injection deviceaccording to a second embodiment.

FIG. 4 shows a general view of the post-injection system incorporated inan engine/particulate filter combination.

The system that permits the putting into practice of the regenerationmethod according to the invention is shown schematically in FIG. 1,according to a preferable embodiment. In this system, various mechanicalcomponents of a particulate filter that does or does not form part ofthe filtration device collaborate in order to permit the control of theregeneration of the filtration system.

Thus the exhaust gases issuing from the diesel engine in the pipe 1, arecontrolled for temperature by the sensor 2 and for pressure by thesensor 3 and are then sent to the oxidation catalyst 4 and then to thefilter cartridges 5, the whole being contained in a metal housing 6 andinsulated by ceramic elements 7.

Whenever necessary, a computer 8 actuates the diesel fuel injectionsfrom the electromagnetic injector 9 mounted on an injector-holder unit10, which is supplied from a bypass of the diesel engine via the line11, the diesel fuel being sent to the exhaust pipe via the capillary 12.

This capillary 12 terminates at the center of the pipe 13 in the exhaustpipe 14 upstream of the oxidation catalyst 4, in order to obtain properspraying by the air that arrives concentrically and which is admitted bythe solenoid valve 15, supplied by a pressure regulator, not shown.

A second solenoid valve 16 serves to purge the capillary to preventdiesel fuel from stagnating in the capillary and from coking and causingits obstruction near the exhaust pipe, which is very hot.

A detailed view of the post-injection device, particularly of theinjector-holder according to a first embodiment, is shown in FIG. 2.

The computer 8, using the temperature and pressure data gathered by thesensors 2 and 3, and depending on the strategy set, actuates a dieselfuel injection from the electromagnetic injector 9 supplied with dieselby the engine circuit at 11. At the outlet of this electromagneticinjector, the volume of diesel injected is sent by the capillary 12 tothe exhaust pipe 1 where it is sprayed at 14 with the air that arrivesconcentrically via the line 13.

The spray air rate is controlled by the solenoid valve 15 supplied by apressure regulator, not shown, its opening is simultaneous with that ofthe injector 11, in order to obtain proper spraying from the outset butits closure is delayed by a few seconds in order to allow the rinsing ofthe capillary by air, which is supplied from the solenoid valve 16 assoon as the injector is closed, a check valve 17 preventing anyaccumulation of diesel fuel in the line of the injector-holder 10 inorder to permit effective rinsing.

A variant of this embodiment is shown in FIG. 3. According to thisvariant, to improve the quality of spraying of the diesel fuel and tosimplify the construction of this assembly, the injector-holder 10 issupplied with air by a single solenoid valve which opens simultaneouslywith the diesel injector 9, but the closure of which is delayed by a fewseconds, as for the previous embodiment, so that the capillary rinsingoperation takes place automatically thanks to the air flow controlled bythe calibrated air nozzle 18. Further, upon the opening of the solenoidvalve 15, this air flow serves to form an emulsion with the diesel fuelissuing from the injector 9 in the chamber 19 and is then sent via thecapillary 12 to the outlet into the exhaust pipe at 14. This emulsionterminates at the center of the tube 13 where it encounters the airstream conveyed by this tube, to be finely sprayed and to obtain muchbetter atomization quality, thanks to the emulsion already formed in thecapillary. On the closure of the injector, the maintenance of the airflow for a few additional seconds serves to completely rinse thecapillary 12.

On this embodiment, good results have been obtained with an air supplypressure of 3 bar, for example, supplied by the solenoid valve 15 via a4/6 mm rilsan tube, for example, and via a restriction at the inlet ofthe injector-holder, e.g. 2 mm in diameter and via a 0.45 mm air nozzle,e.g. to supply the chamber 19 at the inlet of the capillary 12. Thisstainless steel capillary, e.g. of 1/1.6 mm had a length of 50 cm andwas contained in a 4/6 mm stainless steel tube, e.g. the quality of thediesel mist obtained-served to carry out injections up to temperaturesof 270° C. at the catalyst inlet e.g. without observing undesirablehydrocarbon emissions.

FIG. 4 shows the post-injection device associated with a particulatefiltration system, the combination being mounted on a diesel engine 20supplied by an air compressor 21, and discharging through a turbine 22to remove the exhaust gases via a pipe 23, to the system at 1 where thetemperature sensor 2 and pressure sensor 3 are arranged, before sprayingat 14 the diesel fuel with the air issuing from the line 13. Theinjector 9 is supplied by a line 11 mounted on a bypass on the dieselfeed of the engine injection pump 24.

In the particulate filter regeneration method with the post-injectiondevice, if the temperature is insufficient to initiate the combustion ofthe particulates, the regeneration occurs thanks to the dieselinjection.

For this purpose, the temperature in the neighborhood of the catalystinlet is measured, using the sensor 2, e.g. of the thermocouple orthermistor type, arranged at the inlet of the system. The value of thetemperature θ_(m) measured is received by the computer 8. The computercompares this value θ_(m) to a reference value θ_(r), corresponding tothe temperature at which the combustion of the diesel on the catalystwith excess air is complete. A person skilled in the art is perfectlyable to determine θ_(r). In practice, for diesel engines, θ_(r) is forexample ≧300° C.

If the temperature θ_(m) measured is equal to or higher than thereference value θ_(r) the electronic control box initiates the openingof the injector 9 and of the solenoid valve 15. This opening causes theintake of diesel fuel into the capillary and compressed air into thetube 13. At the outlet of the tube 13 at 14, the diesel is mixed withthe compressed air and the mixture thus formed is sprayed in atomizedform into the exhaust gas discharge pipe 1.

The fuel injected into the exhaust pipe 1 enters the chamber 6 andundergoes complete combustion at the catalyst 4. This combustion causesthe temperature to rise significantly to a temperature θ_(c) at whichthe combustion of the particulates clogging the filtration means occurs.The molecules of NO₂ produced in combination with the excess residualoxygen present in the exhaust gases catalyze this oxidation reaction.Thus this reaction occurs at a temperature lower than the normalcombustion temperature.

During this oxidation, the solid particulates are converted to gaseswhich are removed.

The filtration means is then free of deposits and recovers its fullfiltration capacity.

According to a particular embodiment, the measurement of θ_(m) can beused by the electronic control box to evaluate the temperature of theparticulates at the level of the filtration means. In fact, if θ_(m) isclose to the temperature at which combustion of particulates can takeplace without diesel post-injection, the computer can decide not toinitiate this post-injection, thereby achieving a substantial fueleconomy.

Another operational mode consists in simultaneously measuring thetemperature and pressure at the level of the catalyst production meansusing the temperature sensor 2 and the pressure sensor 3. The pressurevalue P_(m) measured reflects the degree of obstruction of thefiltration means by the particulates. In fact, if the filtration meansis clogged, the exhaust gases pass through with greater difficulty andexert a backpressure. Thus the measurement of the pressure P_(m)represents the best means to control the clogging of the filtrationmeans. The sensor 3 is a conventional sensor for measuring the absolutepressure. According to a variant, the pressure sensor 3 may be a sensorfor measuring the gauge pressure, comprising one sensor located upstreamof the filter and another downstream of said filter.

The electronic control box compares the value P_(m) measured to areference value P_(r), corresponding to the maximum acceptable degree ofobstruction of the filtration means. The determination of P_(r)indicating the clogging is carried out easily and arbitrarily by aperson skilled in the art. In practice, and for example, the pressureP_(r) corresponds to the pressure measured with a new filter plus 100mbar.

If P_(m) is equal to or higher than P_(r), the electronic control boxcompares θ_(m) to θ_(r). If θ_(m) is equal to or higher than θ_(r), thecontrol box initiates the post-injection of diesel which leads toregeneration of the filtration means. This operational mode has theadvantage of only initiating post-injection when the filtration meanshas reached a given degree of clogging, thereby serving to considerablylimit the surplus consumption of fuel. With this pressure data, thecomputer, still based on the setpoints, can, depending on thebackpressure level, increase the injection time in order to reach ahigher temperature.

EXAMPLE

As a non-limiting example, a filtration device is used with anindustrial vehicle engine, the Renault VI 620-45 supercharged engine,with 10 liters cylinder displacement and 180 kW horsepower. This engineis used on urban buses.

The filtration device is composed of:

-   -   a platinum based metal oxidation catalyst permitting total        oxidation of CO and hydrocarbons at low temperature, as well as        the conversion of part of the NO to NO₂, the platinum content        was 90 g per cubic foot,    -   Ibiden particulate filters, of the silicon carbide honeycomb        type, mounted in parallel,    -   a diesel injection system according to the second embodiment        shown in FIG. 3, the capillary 12 used was made from stainless        steel, with 1 mm inside diameter by 1.6 mm outside diameter, and        the air intake tube 13 was also made from stainless steel, with        4 mm inside diameter and 6 mm outside diameter, for a total        length of 50 cm,    -   an electronic control box 8 controlling the diesel        post-injection. A timer limits the post-injection time to 20 s        and corresponds to an injected quantity of 20 cm³, followed by        specific programming of the control box in order to further        obtain a post-injection at 7 minute intervals,    -   the electromagnetic injector 9 was supplied by the line 11        connected by a tee to the engine injection pump feed line, in        order to have a feed pressure of between 1 and 1.5 bar.

The electronic control box was regulated so that the post-injection wasinitiated as soon as the backpressure reached 150 mb and the gastemperature was higher than 300° C.

In these configurations, the bus traveled more than 45 000 km withoutobserving any drift in backpressure, demonstrating that thepost-injection system did its job satisfactorily by permanentlymaintaining a sufficient temperature for the regeneration of the filterto take place continuously despite the severe service conditions.

A test was conducted after 15 000 km of travel on a pollution cyclerepresentative of urban traffic conditions on the UTAC roller test benchand yielded the following remarkable results: TYPE L/100 CO2 CO HC NOxParticulates Series 56.7 1420 4.06 1.06 23 0.43 Devices 57.6 1452 0.200.03 21.5 0.03

Emissions in Grams/Kilometer

These results demonstrate the effectiveness of this device, both interms of regeneration and pollution control on all pollutants.

The post-injection method according to the invention, associated with afiltration device using an oxidation catalyst, is hence particularlyadequate for the treatment of the exhaust gases of urban transitvehicles. In fact, the gases produced by these vehicles are generallyproduced at a temperature lower than the temperature necessary to permitregeneration of the conventional filtration devices, causing clogging ofthese devices and hence their rapid deterioration by sudden combustionreactions. However, the results obtained with the present techniqueserved to consider a minimum service life of the filtration device of100 000 km, on vehicles of this type.

Thus, while the injection device according to the invention does notcomprise any novel technical elements, the inventors have the merit ofhaving succeeded in combining and adapting various existing techniquesin order to synergize their effects and to obtain a device which isextremely effective and robust for permitting a reliable dieselpost-injection generating no undesirable hydrocarbon emissions andpermitting a significant increase in the exhaust gas temperature topermit the oxidation of the carbon particulates retained on the filter,and to obtain excellent results in terms of filter regeneration, even inthe case of vehicles in which the engine speeds do not permit theproduction of exhaust gases at high temperature.

1. A method for the post-injection of a regeneration liquid,particularly for the regeneration of a device for filtering exhaustgases produced by a diesel engine, comprising retaining particulates,after being sent to an oxidation catalyst, on a filtration device,wherein: the regeneration liquid comprises at least one hydrocarbonand/or at least one reducing agent, the post-injection consistsessentially in injecting, upstream of the catalyst, using apost-injection device: on the one hand, the regeneration liquid, and onthe other, at least one gaseous fluid, preferably compressed air, thisregeneration liquid and this gaseous fluid together forming an aerosolsuitable for spraying the regeneration liquid into the exhaust gases andfor increasing their temperature, so as to accelerate the oxidation rateof said particulates and thereby contribute to the regeneration of thefiltration device, and wherein the regeneration liquid issuing from aninjector is conveyed by a capillary contained in a line supplied withgaseous fluid, preferably compressed air; the capillary or nozzle andthe line are concentric and coaxial, like their respective openings,which terminate in the exhaust pipe(s).
 2. The method as claimed inclaim 1, wherein a part of the gaseous fluid, preferably compressed air,passes through the same nozzle as the regeneration liquid, up to thepost-injection opening.
 3. The method as claimed in claim 2, wherein apart of the gaseous fluid is mixed with the regeneration liquid beforethe post-injection.
 4. The method as claimed in claim 2, wherein theflow of gaseous fluid, preferably compressed air, is maintained in thepost-injection nozzle, after the interruption of the post-injection ofthe regeneration liquid through this nozzle, and during the timenecessary for rinsing said nozzle.
 5. The method as claimed in claim 1,wherein the temperature of at least a part of the post-injection deviceis kept lower than or equal to 120° C., preferably 100° C., while theengine is running.
 6. The method as claimed in claim 5, wherein at leasta part of the post-injection device is kept at a distance from thepipe(s) in which the exhaust gases flow.
 7. The method as claimed inclaim 1, wherein the regeneration liquid is selected: from the group ofhydrocarbons comprising oil refining products (preferably gasoline anddiesel), from the group of alcohols (preferably methanol), from thegroup of reducing agents (preferably urea and ammoniacal solutions), andmixtures thereof.
 8. The method as claimed in claim 1, furthercomprising: measuring a temperature θ_(m) upstream of the oxidationcatalyst, comparing θ_(m) to a temperature θ_(r) corresponding to thetemperature at which the combustion of the regeneration liquid, in thepresence of the combustion catalyst, is complete, if θ_(m) is equal toor greater than θ_(r), initiating a post-injection of regenerationliquid.
 9. The method as claimed in claim 8, further compromising:measuring a pressure P_(m) upstream of the filtration device by asensor, said pressure P_(m) reflecting the degree of obstruction of thefiltration device by the particulates, comparing said pressure P_(m) toa reference pressure P_(r) corresponding to the maximum acceptabledegree of obstruction, if P_(m) is equal to or greater than the pressureP_(r) and if θ_(m) is equal to or greater than θ_(r), initiating thepost-injection of diesel.
 10. The method as claimed in claim 1, whereinthe diesel injections are controlled, by at least one computer, takingaccount of the temperature θ_(m) data and optionally the pressure P_(m)data, to obtain the temperature increase desired for optimalregeneration of the filtration device.
 11. A device for in particularputting into practice the post-injection method as claimed in claim 1and comprising at least one exhaust pipe, at least one catalyst and afiltration device further comprising: a regeneration liquid supplydevice, a device for supplying pressurized gaseous fluid, preferablycompressed air, a post-injection device including: at least one injectorfit preferably electromagnetic, at least one injector-holder, on whichsaid injector is arranged, at least one capillary or nozzle startingfrom the injector and terminating in at least one exhaust pipe via atleast one opening, upstream of the catalyst, at least one line connectedto the device for supplying pressurized gaseous fluid, preferablycompressed air, and terminating in the exhaust pipe(s) via at least oneopening, the capillary or nozzle and the line are concentric andcoaxial, like their respective openings which terminate in the exhaustpipe(s) in, the capillary or nozzle is contained in the line, optionallyat least one temperature sensor for measuring θ_(m), arranged on theexhaust pipe(s) upstream of the catalyst, optionally at least onepressure sensor for measuring P_(m) in the exhaust pipe(s) and arrangedon said pipe(s) upstream of the catalyst, at least one computer t forcontrolling the post-injection, to which are subjected the regenerationliquid supply device, the device for supplying pressurized gaseousfluid, preferably compressed air, the post-injection means device, andthe temperature or pressure sensor(s), if any.
 12. The device as claimedin claim 11, wherein at least a part of the post-injection device,preferably at least the injector, is designed so that it is preferablyarranged at a sufficient distance from the exhaust pipe(s) to avoidsuffering thermal damage, that is, to remain at a temperature lower thanor equal to 120° C., preferably 100° C., while the engine is running.13. The device as claimed in claim 11, wherein the device for supplyingpressurized gaseous fluid, preferably compressed air, is designed topermit the intake of gaseous fluid at the outlet of the injector, at thehead of the capillary or nozzle, so that the pressurized gaseous fluid,preferably compressed air, can flow with the post-injected regenerationliquid in the capillary or nozzle.
 14. The device as claimed in claim13, wherein the device for supplying pressurized gaseous fluid,preferably compressed air, comprise a solenoid valve controlling theintake of pressurized gaseous fluid, preferably compressed air, at theoutlet of the injector, at the head of the capillary or nozzle, topermit said fluid to flow with the regeneration liquid and, secondarily,to rinse the capillary or nozzle after the end of the post-injection, bymaintaining, for some time, a flow of pressurized gaseous fluid,preferably compressed air, in the capillary or nozzle.
 15. The device asclaimed in claim 11, wherein the device for supplying pressurizedgaseous fluid, preferably compressed air, and the post-injectiondevice—preferably the injector-holder, are designed so that at least onecalibrated orifice is provided for the continuous intake of a flow ofpressurized gaseous fluid, preferably compressed air, mixed with theregeneration liquid, at the inlet of the capillary or nozzle, in orderto produce an emulsion and further and preferably to perform the rinsingfunction, by maintaining, for some time after the closure, a flow ofsaid gaseous fluid in the capillary or nozzle.
 16. The device as claimedin claim 11, wherein the regeneration liquid supply device is connectedto the feed line of at least one mechanical injection pump of theengine.
 17. The device as claimed in claim 11, wherein the regenerationliquid is selected: from the group of hydrocarbons comprising oilrefining products (preferably gasoline and diesel), from the group ofalcohols (preferably methanol), from the group of reducing agents(preferably urea and ammoniacal solutions), and mixtures thereof. 18.The device as claimed in claim 11, further comprising a temperaturesensor and a pressure sensor and wherein the computer which is connectedto the temperature sensor and to the pressure sensor is adapted tocompare the values θ_(m) and optionally P_(m) measured respectively withthe reference values θ_(r) and optionally P_(r), and initiates thepost-injection of regeneration liquid into the exhaust pipe, via theregeneration liquid supply device, the device for supplying pressurizedgaseous fluid, preferably compressed air, and the post-injection device,when the measurements θ_(m) and optionally P_(m) are equal to or higherthan the reference values θ_(r) and optionally P_(r).